POLLUTED runoff from onshore sources is the No. 1 danger to water quality. But the state Department of Ecology’s campaign to create a “no-discharge zone” across 2,000 miles of Puget Sound waters unfairly targets recreational boaters and the maritime community.

There’s a better way.

People of goodwill are on both sides of this issue. It’s time now to step back and let science answer key questions.

There are legitimate concerns over the effectiveness of a no-discharge zone. Even the state Ecology Department, in its draft petition to the U.S. Environmental Protection Agency, acknowledges that only a small portion of the total pollutant load entering the Puget Sound is from boats and ships.

Eighty such zones already exist in American waters, so collecting data proving their worth should be simple. It would be equally useful if agencies produce a model showing what role boaters play in Puget Sound pollution.

It’s already against the law to flush untreated sewage into Puget Sound. According to the state Ecology Department’s own maps, areas where water quality is lowest aren’t areas heavily trafficked by vessels.

Do the research to determine if one large no-discharge zone is really needed. A series of smaller zones covering the most environmentally sensitive areas may be more practical. Start by creating no-discharge zones in places like Whidbey Island’s Penn Cove, Samish Bay near Anacortes and Oakland Bay, where the world’s best oysters grow. Technology exists to warn boaters away from shellfish beds. Can an app be far behind?

Washington state’s proposed 2,000-mile zone would be the nation’s largest, and it would have alarmingly steep costs.

The Department of Ecology’s plan prohibits these devices, forcing boat-owners to abandon current technology and retrofit vessels with onboard storage tanks, sacrificing fuel or cargo space.

The tanks would need to be pumped out to shoreline facilities for treatment, adding fuel costs, increasing work hours and reducing efficiency.

Costs do matter. For a typical tugboat — and more than 150 tugs work in the proposed zone — a retrofit would cost $125,000 or more. Retrofit costs are prohibitive for some owners. It is unclear whether they could continue to operate their boats locally.

Could commercial fishing boats abandon Fisherman’s Terminal for Alaska or Canada? These vessels are here because we have a robust maritime economy — shipyards, freshwater maintenance facilities and a pool of experienced mariners. If boats leave, those enterprises and sailors suffer.

The Department of Ecology has hinted money is available for retrofits. But the state is already having trouble financing schools. Boats will be a low priority in the next legislative session.

Retrofitting won’t be the only costs involved. The EPA requires a sufficient number of pumpout facilities to accommodate the number of impacted vessels. The only commercial shore-side pumpout facilities are for the exclusive use of Washington State Ferries. Building this infrastructure from scratch would take time and money.

Here, too, the Department of Ecology says state government dollars might be available. Or not.

Close to 20 years of my public-service life have been with agencies that work with mariners. We didn’t always see eye to eye. But the sector has a history of acting in good faith to ensure water quality. The state Department of Ecology should heed maritime concerns and partner to develop no-discharge zones that protect everyone’s interests.

Bob Edwards previously served on the Port of Seattle Commission, the Puget Sound Regional Council, the Puget Sound Water Quality Authority and was president of the Association of Washington Cities.